Compensation for electrical converter nonlinearities

ABSTRACT

Systems and methods are provided for delivering energy from an input interface to an output interface. An electrical system includes an input interface, an output interface, an energy conversion module coupled between the input interface and the output interface, and a control module. The control module determines a duty cycle control value for operating the energy conversion module to produce a desired voltage at the output interface. The control module determines an input power error at the input interface and adjusts the duty cycle control value in a manner that is influenced by the input power error, resulting in a compensated duty cycle control value. The control module operates switching elements of the energy conversion module to deliver energy to the output interface with a duty cycle that is influenced by the compensated duty cycle control value.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Agreement No.DE-FC26-07NT43123, awarded by the United States Department of Energy.The Government has certain rights in this invention.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally toelectrical systems in automotive vehicles, and more particularly,embodiments of the subject matter relate to bidirectional energydelivery systems with galvanic isolation.

BACKGROUND

Matrix converters may be used in electric and/or hybrid vehicles toaccommodate delivery of relatively high power over a relatively widerange of operating voltages, while at the same time achieving galvanicisolation, relatively high power factors, low harmonic distortion,relatively high power density and low cost. For example, bidirectionalisolated matrix converters may be used to deliver energy from analternating current (AC) energy source, such as the single-phase gridelectricity common in most residential and commercial buildings, tocharge a direct current (DC) energy storage element, such as arechargeable battery, in a vehicle. However, nonlinear power lossesattributable to components of the matrix converter, such as transistorswitches or diodes, may limit the accuracy and effectiveness of existingcontrol strategies.

BRIEF SUMMARY

In accordance with one embodiment, an electrical system is provided. Theelectrical system includes an input interface, an output interface, anenergy conversion module coupled between the input interface and theoutput interface, and a control module coupled to the energy conversionmodule, the input interface, and the output interface. The energyconversion module includes one or more switching elements. The controlmodule is configured to determine a duty cycle control value foroperating the energy conversion module to produce a desired voltage atthe output interface. The control module determines an input power errorat the input interface and adjusts the duty cycle control value in amanner that is influenced by the input power error, resulting in acompensated duty cycle control value. The control module operates theswitching elements of the energy conversion module to deliver energy tothe output interface with a duty cycle that is influenced by thecompensated duty cycle control value.

In accordance with another embodiment, a method is provided for using anenergy conversion module to deliver energy from an input interface to anoutput interface. The method comprises the steps of determining an inputpower reference for the input interface based on a desired outputvoltage at the output interface and determining a duty cycle controlvalue based on the input power reference. The method continues bydetermining an input power error based on a difference between anestimated input power at the input interface and the input powerreference, adjusting the duty cycle control value in a manner that isinfluenced by the input power error to obtain a compensated duty cyclecontrol value, and operating one or more switching elements of theenergy conversion module to deliver energy from the input interface tothe output interface with a duty cycle influenced by the compensatedduty cycle control value.

In another embodiment, an electrical system is provided. The electricalsystem comprises a DC interface, an AC interface, an isolation moduleincluding a first set of windings magnetically coupled to a second setof windings, a first energy conversion module coupled between the DCinterface and the first set of windings, a second conversion modulecoupled to the second set of windings, an inductive element coupledbetween the second conversion module and the AC interface, and a controlmodule coupled to the second conversion module. The control module isconfigured to determine an input power reference for producing a desiredvoltage at the DC interface based on the desired voltage and a measuredvoltage at the DC interface, determine an input power error at the ACinterface based on a difference between an estimated input power at theAC interface and the input power reference, and determine a compensatedpulse-width modulation (PWM) duty cycle control value for operating thefirst energy conversion module based on the input power reference andthe input power error. The control module operates switches of thesecond conversion module in accordance with the compensated PWM dutycycle control value.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a schematic view of a electrical system suitable for use in avehicle in accordance with one embodiment;

FIG. 2 is a block diagram of a control system suitable for use with theelectrical system of FIG. 1 in accordance with one embodiment; and

FIG. 3 is a flow diagram of control process suitable for use with theelectrical system of FIG. 1 in accordance with one embodiment.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

Technologies and concepts discussed herein relate generally toelectrical converters capable of delivering energy from an alternatingcurrent (AC) interface to a direct current (DC) interface. As describedin greater detail below, a feedforward control scheme is used todetermine an input voltage reference for the input voltage at the ACinterface based on a desired output voltage at the DC interface and ameasured voltage at the DC interface, and a pulse-width modulation (PWM)duty cycle control value for operating the electrical converter isdetermined based on a ratio of the input voltage reference to themeasured voltage at the DC interface. In an exemplary embodiment, thePWM duty cycle control value is scaled using a compensation scalingfactor that decreases the PWM duty cycle control value in a manner thataccounts for component power losses.

FIG. 1 depicts an exemplary embodiment of an electrical system 100 (oralternatively, a charging system, charger or charging module) suitablefor use in a vehicle, such as, for example, an electric and/or hybridvehicle. The electrical system 100 includes, without limitation, a firstinterface 102, a first energy conversion module 104, an isolation module106, a second energy conversion module 108, an inductive element 110, acapacitive element 112, a second interface 114, and a control module116. The first interface 102 generally represents the physical interface(e.g., terminals, connectors, and the like) for coupling the electricalsystem 100 to a DC energy source 118 and the second interface 114generally represents the physical interface (e.g., terminals,connectors, and the like) for coupling the electrical system 100 to anAC energy source 120. Accordingly, for convenience, the first interface102 may be referred to herein as the DC interface and the secondinterface 114 may be referred to herein as the AC interface. In anexemplary embodiment, the control module 116 is coupled to the energyconversion modules 104, 108 and operates the energy conversion modules104, 108 to deliver energy (or power) from the AC energy source 120 tothe DC energy source 118 to achieve a desired DC output voltage(V_(REF)) at the DC interface 102, as described in greater detail below.

In an exemplary embodiment, the DC energy source 118 (or alternatively,the energy storage source or ESS) is capable of receiving a directcurrent (indicated by arrow 150) from the electrical system 100 at aparticular DC voltage level (indicated by arrow 160). In accordance withone embodiment, the DC energy source 118 is realized as a rechargeablehigh-voltage battery pack having a nominal DC voltage range from about200 to about 500 Volts DC. In this regard, the DC energy source 118 maycomprise the primary energy source for another electrical system and/oran electric motor in a vehicle. For example, the DC energy source 118may be coupled to a power inverter that is configured to provide voltageand/or current to the electric motor, which, in turn, may engage atransmission to drive the vehicle in a conventional manner. In otherembodiments, the DC energy source 118 may be realized as a battery, anultracapacitor, or another suitable energy storage element.

The AC energy source 120 (or power source) is configured to provide anAC current (indicated by arrow 170) to the electrical system 100 at aparticular AC voltage level (indicated by arrow 180) and may be realizedas a main power supply or main electrical system for a building,residence, or another structure within an electric power grid (e.g.,mains electricity or grid power). In accordance with one embodiment, theAC energy source 120 comprises a single-phase power supply, as is commonto most residential structures, which varies depending on the geographicregion. For example, in the United States, the AC energy source 120 maybe realized as 120 Volts (RMS) or 240 Volts (RMS) at 60 Hz, while inother regions the AC energy source 120 may be realized as 110 Volts(RMS) or 220 Volts (RMS) at 50 Hz. In alternative embodiments, the ACenergy source 120 may be realized as any AC energy source suitable foroperation with the electrical system 100.

As described in greater detail below, the DC interface 102 is coupled tothe first energy conversion module 104 and the AC interface 114 iscoupled to the second energy conversion module 108 via the inductiveelement 110. The isolation module 106 is coupled between the energyconversion modules 104, 108 and provides galvanic isolation between thetwo energy conversion modules 104, 108. The control module 116 iscoupled to the energy conversion modules 104, 108 and operates thesecond energy conversion module 108 to convert energy from the AC energysource 120 to high-frequency energy across the isolation module 106which is then converted to DC energy at the DC interface 102 by theenergy conversion module 104. It should be understood that although thesubject matter may be described herein in the context of agrid-to-vehicle application (e.g., the AC energy source 120 deliveringenergy to the DC energy source 118) for purposes of explanation, inother embodiments, the subject matter described herein may beimplemented and/or utilized in vehicle-to-grid applications (e.g., theDC energy source 118 delivering energy to the AC interface 114 and/or ACenergy source 120). For convenience, but without limitation, the ACinterface 114 may alternatively be referred to herein as the inputinterface and the DC interface 102 may alternatively be referred toherein as the output interface in the context of a grid-to-vehicleapplication.

In order to deliver energy to (or charge) the DC energy source 118, thefirst energy conversion module 104 converts the high-frequency energy atnodes 122, 124 to DC energy that is provided to the DC energy source 118at the DC interface 102. In this regard, the first energy conversionmodule 104 operates as a rectifier when converting high frequency ACenergy to DC energy. In the illustrated embodiment, the first energyconversion module 104 comprises four switching elements 9-12 with eachswitching element having a diode 29-32 configured antiparallel to therespective switching element to accommodate bidirectional energydelivery. As shown, a capacitor 126 is configured electrically inparallel across the DC interface 102 to reduce voltage ripple at the DCinterface 102, as will be appreciated in the art.

In an exemplary embodiment, the switching elements 9-12 are transistors,and may be realized using any suitable semiconductor transistor switch,such as a insulated gate bipolar transistor (IGBT), a field-effecttransistor (e.g., a MOSFET or the like), or any other comparable deviceknown in the art. The switches and diodes are antiparallel, meaning theswitch and diode are electrically in parallel with reversed or inversepolarity. The antiparallel configuration allows for bidirectionalcurrent flow while blocking voltage unidirectionally, as will beappreciated in the art. In this configuration, the direction of currentthrough the switches is opposite to the direction of allowable currentthrough the respective diodes. The antiparallel diodes are connectedacross each switch to provide a path for current to the DC energy source118 for charging the DC energy source 118 when the respective switch isoff.

In the illustrated embodiment, switch 9 is connected between node 128 ofthe DC interface 102 and node 122 and configured to provide a path forcurrent flow from node 128 to node 122 when switch 9 is closed. Diode 29is connected between node 122 and node 128 and configured to provide apath for current flow from node 122 to node 128 (e.g., diode 29 isantiparallel to switch 9). Switch 10 is connected between node 130 ofthe DC interface 102 and node 122 and configured to provide a path forcurrent flow from node 122 to node 130 when switch 10 is closed, whilediode 30 is connected between node 122 and node 130 and configured toprovide a path for current flow from node 130 to node 122. In a similarmanner, switch 11 is connected between node 128 and node 124 andconfigured to provide a path for current flow from node 128 to node 124when switch 11 is closed, diode 31 is connected between node 124 and theDC interface 102 and configured to provide a path for current flow fromnode 124 to node 128, switch 12 is connected between node 130 and node124 and configured to provide a path for current flow from node 124 tonode 130 when switch 12 is closed, and diode 32 is connected betweennode 124 and the DC interface 102 and configured to provide a path forcurrent flow from the node 130 to node 124.

In an exemplary embodiment, the second energy conversion module 108facilitates the flow of current (or energy) from the AC energy source120 and/or inductive element 110 to the isolation module 106. In theillustrated embodiment, the second energy conversion module 108 isrealized as a front end single-phase matrix conversion module comprisingeight switching elements 1-8 with each switching element having a diode21-28 configured antiparallel to the respective switching element, in asimilar manner as set forth above in regards to the first energyconversion module 104. For convenience, but without limitation, thesecond energy conversion module 108 may alternatively be referred toherein as a matrix conversion module. As described in greater detailbelow, the control module 116 modulates (e.g., opens and/or closes) theswitches 1-8 of the matrix conversion module 108 in accordance with aPWM duty cycle control value to produce a high-frequency voltage atnodes 134, 136 that results in a power flow to the DC interface 102and/or DC energy source 118 intended to achieve a desired output voltageat the DC interface 102.

In the illustrated embodiment of FIG. 1, a first pair of switches 1, 2and diodes 21, 22 are coupled between node 132 and node 134, with thefirst pair of switch and antiparallel diode (e.g., switch 1 and diode21) being configured with opposite polarity to the second pair of switchand antiparallel diode (e.g., switch 2 and diode 22). In this manner,switch 1 and diode 22 are configured to provide a path for current flowfrom node 134 through switch 1 and diode 22 to node 132 when switch 1 isclosed, turned on, or otherwise activated and the voltage at node 134 ismore positive than the voltage at node 132. Switch 2 and diode 21 areconfigured to provide a path for current flow from node 132 throughswitch 2 and diode 21 to node 134 when switch 2 is closed, turned on, orotherwise activated and the voltage at node 132 is more positive thanthe voltage at node 134. In a similar manner, a second pair of switches3, 4 and diodes 23, 24 are coupled between node 136 and node 138, athird pair of switches 5, 6 and diodes 25, 26 are coupled between node132 and node 136, and a fourth pair of switches 7, 8 and diodes 27, 28are coupled between node 134 and node 138.

In the illustrated embodiment, switches 1, 3, 5, and 7 comprise a firstset of switches which are capable of commutating the current through theinductive element 110 (i_(L)) (indicated by arrow 190) from node 138 tonode 132 when the current through the inductive element 110 is flowingin a negative direction (e.g., i_(L)<0) and switches 2, 4, 6, and 8comprise a second set of switches that are capable of commutating thecurrent through the inductive element 110 from node 132 to node 138 whenthe current through the inductive element 110 is flowing in a positivedirection (e.g., i_(L)0), as described in greater detail below. In otherwords, switches 1, 3, 5, 7 are capable of conducting at least a portionof current flowing in a negative direction through the inductive element110 (e.g., i_(L)<0) and switches 2, 4, 6, 8 are capable of conducting atleast a portion of current flowing in a positive direction through theinductive element 110 (e.g., i_(L)>0). As used herein, commutatingshould be understood as the process of cycling the current through theinductive element 110 through switches and diodes of the matrixconversion module 108 such that the flow of current through theinductive element 110 is not interrupted.

In an exemplary embodiment, the isolation module 106 comprises a firstset of windings 144 connected between nodes 122, 124 of the first energyconversion module 104 and a second set of windings 146 connected betweennodes 134, 136. For purposes of explanation, the windings 146 may bereferred to herein as comprising the primary winding stage (or primarywindings) and the sets of windings 144 may be referred to herein ascomprising the secondary winding stage (or secondary windings). Thewindings 144, 146 provide inductive elements that are magneticallycoupled in a conventional manner to form a transformer, as will beappreciated in the art. In an exemplary embodiment, the isolation module106 is realized as a high-frequency transformer. In this regard, theisolation module 106 comprises a transformer designed for a particularpower level at a high-frequency, such as the switching frequency of theswitches of the energy conversion modules 104, 108 (e.g., 50 kHz),resulting in the physical size of the transformer being reduced relativeto a transformer designed for the same power level at a lower frequency,such as the frequency of the AC energy source 120 (e.g., the mainsfrequency).

In an exemplary embodiment, the inductive element 110 is realized as aninductor configured electrically in series between node 132 of thematrix conversion module 108 and a node 140 of the AC interface 114.Accordingly, for convenience, but without limitation, the inductiveelement 110 is referred to herein as an inductor. The inductor 110functions as a high-frequency inductive energy storage element duringoperation of the electrical system 100. The capacitive element 112 isrealized as a capacitor coupled between node 140 and node 142 of the ACinterface 114, that is, the capacitor 112 is configured electricallyparallel to the AC interface 114. The capacitor 112 and inductor 110 arecooperatively configured to provide a high frequency filter to minimizevoltage ripple at the AC interface 114 attributable to modulatingswitches 1-8.

The control module 116 generally represents the hardware, firmwareand/or software configured to operate and/or modulate the switches ofthe energy conversion modules 104, 108 to achieve a desired power flowfrom the AC energy source 120 to the DC energy source 118. Depending onthe embodiment, the control module 116 may be implemented or realizedwith a general purpose processor, a microprocessor, a microcontroller, acontent addressable memory, a digital signal processor, an applicationspecific integrated circuit, a field programmable gate array, anysuitable programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof, designed tosupport and/or perform the functions described herein.

During normal operation for grid-to-vehicle applications, the controlmodule 116 determines PWM command signals that control the timing andduty cycles of the switches 1-8 of the matrix conversion module 108 toproduce a high-frequency AC voltage across the primary windings 146 ofthe isolation module 106. The high-frequency AC voltage across theprimary windings 146 induces a voltage across the secondary windings 144at nodes 122, 124 that results in a desired current flowing to the DCinterface 102 to charge or otherwise deliver energy to the DC energysource 118. As described in greater detail below, the control module 116generates a PWM duty cycle control value that controls the duty cycle ofthe switches 1-8 to implement the appropriate switching pattern during aswitching interval (e.g., the inverse of the switching frequency).During the switching interval (or PWM cycle), the control module 116alternates between operating the switches 1-8 to effectivelyshort-circuit nodes 132, 138 and cycle energy through the matrixconversion module 108 to apply a voltage across the inductor 110 beforeoperating the switches 1-8 to release the stored energy and/or voltageof the inductor 110 (alternatively, the fly-back voltage). The sum ofthe fly-back voltage and the input voltage 180 at the AC interface 114is applied to the primary windings 146 of the isolation module 106,resulting in a power transfer to nodes 122, 124 and/or DC energy source118. In this manner, the control module 116 operates the switches 1-8 ofthe matrix conversion module 108 to alternate between cycling energythrough the inductor 110 and delivering energy to the DC interface 102.As described in greater detail below, the percentage of the switchinginterval (or PWM cycle) that the matrix conversion module 108 isdelivering energy to the DC interface 102 corresponds to the duty cycleof the matrix conversion module 108 during that respective switchinginterval.

In an exemplary embodiment, the control module 116 obtains or otherwisemonitors the current 190 through the inductor 110 (e.g., a measuredinductor current (i_(L)) via a current sensor electrically in serieswith the inductor 110), the current (indicated by arrow 185) through thecapacitor 112 (e.g., a measured capacitor current (i_(CAP)) via acurrent sensor electrically in series with the capacitor 112), the inputvoltage 180 at the AC interface 114, and the output voltage 160 at theDC interface 102, and implements a feedforward control system todetermine a PWM duty cycle control value for operating the switches 1-8of the matrix conversion module 108, as described in greater detailbelow. In an exemplary embodiment, the control module 116 obtainsmeasured instantaneous values for the inductor current (i_(L)), thecapacitor current (i_(CAP)), the input voltage (V_(AC)) at the inputinterface 114, and the output voltage (V_(DC)) at the output interface102 that are sampled, measured, or otherwise obtained at a particularinstant in time during a current PWM cycle, wherein the PWM duty cyclecontrol value determined by the control module 116 governs operation ofthe electrical converter during the subsequent PWM cycle. As describedin greater detail below, in an exemplary embodiment, the feedforwardcontrol system implemented by the control module 116 generates acompensated PWM duty cycle control value that is scaled in a manner thataccounts for voltage drops and/or energy losses across the switches 1-8,diodes 21-32 and isolation module 106 (or windings 144, 146) whenoperating the switches 1-8 of the matrix conversion module 108 toalternate between delivering energy and cycling energy through theinductor 110.

It should be understood that FIG. 1 is a simplified representation of anelectrical system 100 for purposes of explanation and is not intended tolimit the scope or applicability of the subject matter described hereinin any way. Thus, although FIG. 1 depicts direct electrical connectionsbetween circuit elements and/or terminals, alternative embodiments mayemploy intervening circuit elements and/or components while functioningin a substantially similar manner. Additionally, although the electricalsystem 100 is described herein in the context of a matrix conversionmodule 108 for a vehicle, the subject matter is not intended to belimited to vehicular and/or automotive applications, and the subjectmatter described herein may be implemented in other applications wherean energy conversion module is utilized to transfer energy usingswitching elements or in other electrical systems where feedforwardcontrol schemes are utilized to achieve power factor correction bymodeling the input port as a loss-free resistor.

FIG. 2 depicts an exemplary embodiment of a feedforward control system200 suitable for use by the control module 116 of FIG. 1. The controlsystem 200 is configured to determine a compensated PWM duty cyclecontrol value (U_(C)) for operating the matrix conversion module 108 toprovide a desired DC output voltage (V_(REF)) at the DC interface 102.In this regard, the compensated PWM duty cycle control value (U_(C))governs the duty cycle (d) for operating matrix conversion module 108during a subsequent PWM cycle (or switching interval), which in turn,governs the respective timing and duty cycles of the switches 1-8 of thematrix conversion module 108 for implementing a desired switchingpattern. The compensated PWM duty cycle control value is a value betweenzero and one that is equal to one minus the duty cycle (U_(C)=1−d), oralternatively, the duty cycle is equal to one minus the compensated PWMduty cycle control value (d=1−U_(C)). In this manner, the duty cycle isinfluenced by the compensated PWM duty cycle control value.

In an exemplary embodiment, the feedforward control system 200 includesa first summation block 202 configured to generate an output energyerror value based on a difference between a desired energy output at afirst input 204 and a measured energy output at a second input 206. Inan exemplary embodiment, the desired energy output at the DC interface102 is calculated or otherwise determined based on the desired DC outputvoltage (V_(REF)), for example, by squaring the desired DC outputvoltage (V_(REF) ²), and the measured energy output at the DC interface102 is calculated or otherwise determined based on the measuredinstantaneous output voltage (V_(DC)), for example, by squaring themeasured instantaneous output voltage (V_(DC) ²). The output energyerror value is provided to the input of a power regulation block 208.The power regulation block 208 generates a desired AC input powerreference value for producing the desired DC output power at the DCinterface 102 based on the output energy error value.

In the illustrated embodiment, the desired AC input power referencevalue is provided to a current conversion block 210 that converts thedesired AC input power reference value to an AC input current referencevalue representative of the required AC current at the AC interface 114for producing the desired AC input power. The AC input current referencevalue corresponds to an AC input current at the AC interface 114 that issubstantially in-phase with the AC input voltage 180 at the AC interface114 to provide substantially unity power factor while producing thedesired AC input power. In an exemplary embodiment, the currentconversion block 210 generates or otherwise determines the AC inputcurrent reference value by multiplying the AC input power referencevalue by the measured AC voltage 180 at the AC interface 114 divided bythe square of the root-mean-square (RMS) voltage at the AC interface114.

In the illustrated embodiment, a second summation block 212 isconfigured to generate or otherwise provide an inductor current errorvalue based on the difference between the measured inductor current(i_(L)) and an inductor current reference value. In an exemplaryembodiment, the second summation block 212 estimates or otherwisedetermines the inductor current reference value as the differencebetween the AC input current reference value and the measured capacitorcurrent (i_(CAP)) received at input 216. The second summation block 212subtracts the inductor current reference value from the measuredinductor current (i_(L)) received at input 214 to generate or otherwiseobtain the inductor current error value, and provides the inductorcurrent error value to a gain block 218 which multiplies the inductorcurrent error value by a gain factor to translate or otherwise convertthe inductor current error value to an AC input voltage error value. Athird summation block 220 is configured to generate an AC input voltagereference value by adding the AC input voltage error value to themeasured AC voltage (V_(AC)) at the AC interface 114, which is providedat input 222.

In the illustrated embodiment, the control system 200 includes adivision block 224 configured to divide the AC input voltage referencevalue from the output of the third summation block 220 by the measuredinstantaneous output voltage (V_(DC)) provided at input 226 to obtain anuncompensated PWM duty cycle control value (U). In an exemplaryembodiment, the AC input voltage reference value is divided by ameasured instantaneous value of the DC voltage 160 at the DC interface102, that is, the most recently sampled DC voltage 160 measured orotherwise obtained during the current PWM cycle (or current switchinginterval). In this regard, the output voltage 160 at the DC interface102 includes both a DC voltage component and an AC voltage component atthe second harmonic of the AC input frequency, for example, a DC voltagewith a superimposed 120 Hz AC voltage for a 60 Hz AC energy source 120coupled to AC interface 114. Thus, using a measured instantaneous DCoutput voltage (V_(DC)) to determine the output energy error value(e.g., by providing the square of the measured DC output voltage atinput 206) introduces harmonic component that is reflected by the ACinput voltage error value, which results in the AC input voltagereference value at the output of the third summation block 220 includinga harmonic component. Dividing the AC input voltage reference value bythe measured instantaneous DC output voltage (V_(DC)), which alsoincludes the harmonic component, effectively cancels or otherwiseeliminates the effect of the harmonic component on the uncompensated PWMduty cycle control value (U). As a result, the total harmonic distortionat the AC interface 114 is reduced. As described in greater detailbelow, the uncompensated PWM duty cycle control value (U) generated bythe division block 224 is provided to a multiplication block 228configured to multiply the uncompensated PWM duty cycle control value bya compensation scaling factor to obtain the compensated PWM duty cyclecontrol value (U_(C)) at the output 230.

In an exemplary embodiment, the control system 200 includes a powerestimation block 232 configured to determine or otherwise estimate theAC input power at the AC interface 114 and provide the result to afourth summation block 234. For example, the power estimation block 232may estimate the AC input power at the AC interface 114 by multiplyingthe measured AC voltage (V_(AC)) at the AC interface 114 provided atinput 236 by the sum of the measured inductor current (i_(L)) providedat input 238 and the measured capacitor current (i_(CAP)) provided atinput 240. The fourth summation block 234 is configured to generate anAC input power error value based on a difference between the estimatedAC input power value and the desired AC input power reference value, forexample, by subtracting the desired AC input power reference value fromthe output of the power regulation block 208 from the estimated AC inputpower signal from the output of the power estimation block 232.

In an exemplary embodiment, the AC input power error value is providedto a proportional-integral (PI) gain block 242 that converts the ACinput power error value to a compensation scaling factor for adjustingor otherwise modifying the PWM duty cycle control value. As describedabove, the PWM duty cycle control value is multiplied by thecompensation scaling factor at multiplication block 228 to obtain thecompensated PWM duty cycle control value at the output 230. Thecoefficients of the PI gain block 242 are configured to generate acompensation scaling factor that is less than one, and approaches one asthe AC input power error value approaches zero. In this manner, thecompensation scaling factor reduces the PWM duty cycle control value andincreases the duty cycle for operating the switches 1-8 of the matrixconversion module 108 in a manner that accounts for component losses inthe charging system 100. For example, in the absence of the compensationscaling factor, unaccounted for component power losses within thecharging system 100 may result in an uncompensated PWM duty cyclecontrol value that provides a duty cycle for operating the switches 1-8of the matrix conversion module 108 that is less than the duty cyclethat is actually needed to overcome the component losses to produce thedesired DC output voltage at the DC interface 102, which, in turn, mayreduce the bandwidth and limit the dynamic performance of the controlsystem.

Referring now to FIG. 3, in an exemplary embodiment, an electricalsystem may be configured to perform a control process 300 and additionaltasks, functions, and operations described below. The various tasks maybe performed by software, hardware, firmware, or any combinationthereof. For illustrative purposes, the following description may referto elements mentioned above in connection with FIGS. 1-2. In practice,the tasks, functions, and operations may be performed by differentelements of the described system, such as the control module 116, thecontrol system 200, and/or the matrix conversion module 108. It shouldbe appreciated that any number of additional or alternative tasks may beincluded, and may be incorporated into a more comprehensive procedure orprocess having additional functionality not described in detail herein.

Referring to FIG. 3, and with continued reference to FIGS. 1-2, in anexemplary embodiment, the control process 300 is performed in responseto an interrupt request that is generated or otherwise received by thecontrol module 116 at fixed regular intervals. For example, inaccordance with one embodiment, the control module 116 receives aninterrupt signal every twenty microseconds that causes the controlmodule 116 to execute the control process 300. The control initializesor begins by obtaining measured values for the input voltage at theinput interface, the output voltage at the output interface, the currentthrough the capacitor, and the current through the inductor (tasks 302,304, 306, 308). In this regard, the control module 116 and/or controlsystem 200 obtains instantaneous values for the input voltage 180 at theAC interface 114, the output voltage 160 at the DC interface 102, thecurrent 185 through capacitor 112, and the current 190 through inductor110 by sampling, sensing, or otherwise measuring the respective valuesduring a current PWM cycle (or switching interval), resulting in ameasured AC input voltage (V_(AC)), a measured DC output voltage(V_(DC)), a measured capacitor current (i_(CAP)), and a measuredinductor current (i_(L)).

In an exemplary embodiment, the control process 300 continues byidentifying or otherwise determining a desired output voltage for thecharging system at the output interface (task 310). For example, inaccordance with one embodiment, the control module 116 may identify adesired value (V_(REF)) for the DC output voltage 160 at the DCinterface 102 in response to receiving a command signal indicative ofthe desired DC output voltage (V_(REF)) from a controller associatedwith the DC energy source 118 (e.g., a battery controller). In anotherembodiment, the control module 116 may be preconfigured or otherwiseassume that the desired DC output voltage 160 will always be equal to aconstant value (e.g., an anticipated or expected voltage for the DCenergy source 118).

After identifying the desired voltage at the DC interface, the controlprocess 300 continues by determining an input power reference for theinput interface based on the desired output voltage at the outputinterface (task 312). As described above, in an exemplary embodiment,the control module 116 and/or control system 200 determines an outputenergy error value based on a difference between a square of the desiredDC output voltage (V_(REF) ²) and a square of the measured DC outputvoltage (V_(DC) ²), and generates a desired input power reference valuefor producing the desired voltage (V_(REF)) at the DC interface 102based on the output energy error value.

In an exemplary embodiment, the control process 300 continues bydetermining an uncompensated PWM duty cycle control value for operatingthe matrix conversion module based on the input power reference value(task 314). In this regard, in an exemplary embodiment, The controlmodule 116 and/or control system 200 converts the desired input powerreference value to an AC input current reference value, subtracts themeasured capacitor current (i_(CAP)) from the AC input current referencevalue to obtain an inductor current reference value, and subtracts theinductor current reference value from the measured inductor current(i_(L)) to obtain an inductor current error value. The control module116 and/or control system 200 multiplies the inductor current errorvalue by a gain factor to translate or otherwise convert the inductorcurrent error value to an AC input voltage error value that is added tothe measured AC input voltage (V_(AC)) to obtain an AC input voltagereference value. It will be appreciated in the art that the gain factormay be selected or otherwise chosen to provide a desired bandwidth forthe control system 200. The control module 116 and/or control system 200continues by dividing the AC input voltage reference value by themeasured DC output voltage (V_(DC)), that is, an instantaneous value forthe output voltage 160 at the DC interface 102 obtained during thecurrent PWM cycle (or switching interval), to obtain the uncompensatedPWM duty cycle control value for operating the matrix conversion module108 during the next PWM cycle.

In an exemplary embodiment, the control process 300 determines an inputpower error value and adjusts the uncompensated PWM duty cycle controlvalue in a manner that is influenced by the input power error value toobtain a compensated PWM duty cycle control value (tasks 316, 318). Inthis regard, as described above, the control module 116 and/or controlsystem 200 determines or otherwise estimates the input power at the ACinterface 114 by multiplying the measured AC input voltage (V_(AC)) bythe measured AC input current, that is, the sum of the measuredcapacitor current (i_(CAP)) and the measured inductor current (i_(L))).The control module 116 and/or control system 200 continues bysubtracting the AC input power reference value from the estimated inputpower value to obtain the input power error value. As described above,the input power error value is provided to a PI gain block 242 to obtaina compensation scaling factor that is less than one. The uncompensatedPWM duty cycle control value is then multiplied by the compensationscaling factor to obtain a compensated PWM duty cycle control value. Inthis manner, the compensation scaling factor decreases the PWM dutycycle control value (or increases the duty cycle) in a manner thataccounts for component losses based on the input power error.

The control process 300 continues by determining PWM command signals foroperating the switches of the matrix conversion module based on thecompensated PWM duty cycle control value for the matrix conversionmodule, and operating the switches of the matrix conversion module inaccordance with the PWM command signals (tasks 320, 322). In thisregard, the control module 116 determines PWM command signals foroperating switches 1-8 during the next PWM cycle such that the matrixconversion module 108 delivers energy from the AC interface 114 to theDC interface 102 during the next PWM cycle at a duty cycle (d) equal toone minus the compensated PWM duty cycle control value (d=1−U_(C)).During the next PWM cycle, the control module 116 operates the switches1-8 of the matrix conversion module 108 in accordance with the PWMcommand signals to deliver energy from the AC interface 114 to the DCinterface 102 for a percentage of the PWM cycle corresponding to theduty cycle (d). In this regard, the control module 116 operates theswitches 1-8 of the matrix conversion module 108 to cycle or otherwisecirculate the inductor current through the matrix conversion module 108without delivering energy to the DC interface 102 for a percentage ofthe PWM cycle corresponding to the compensated PWM duty cycle controlvalue (U_(C)).

For example, referring again to FIG. 1, when the voltage at the ACinterface 114 is positive, the control module 116 concurrently closes(or turns on) switches 2, 4, 6 and 8 to cycle or otherwise circulate theinductor current (i_(L)) through the matrix conversion module 108 for afirst time period (t₁) corresponding to a first portion of the PWMcycle. Switches 2 and 6 and diodes 21 and 25 each conduct at least aportion of the inductor current (i_(L)) at node 132, and switches 8 and4 and diodes 27 and 23 each conduct the portion of the inductor currentflowing through switches 2 and 6 and diodes 21 and 25, respectively, tonode 138. The control module 116 subsequently opens (or turns off)switches 6 and 8 while maintaining switches 2 and 4 in a closed state toconduct the inductor current (i_(L)) from node 132 to node 138 throughthe primary windings 146 and apply a voltage across the primary windings146, thereby delivering energy to the DC interface 102 (via secondarywindings 144 and the energy conversion module 104) for a second timeperiod (t₂) corresponding to a second portion of the PWM cycle. Thecontrol module 116 then concurrently closes (or turns on) switches 2, 4,6 and 8 to cycle or otherwise circulate the inductor current (i_(L)))through the matrix conversion module 108 for a third time period (t₃)corresponding to a third portion of the PWM cycle. The control module116 subsequently opens (or turns off) switches 2 and 4 while maintainingswitches 6 and 8 in a closed state to conduct the inductor current(i_(L)) from node 132 to node 138 through the primary windings 146 andapply a voltage across the primary windings 146 and thereby deliverenergy to the DC interface 102 (via secondary windings 144 and theenergy conversion module 104) for a fourth time period (t₄)corresponding to the remaining portion of the PWM cycle. The sum of thefour time periods correspond to the duration of the PWM cycle, whereinthe sum of the first time period and the third time period divided bythe sum of the four time periods corresponds to the compensated PWM dutycycle control value

$\left( {{e.g.},{U_{C} = \frac{t_{1} + t_{3}}{t_{1} + t_{2} + t_{3} + t_{4}}}} \right)$

and the sum of the second time period and the fourth time period dividedby the sum of the four time periods corresponds to the duty cycle

$\left( {{e.g.},{d = \frac{t_{2} + t_{4}}{t_{1} + t_{2} + t_{3} + t_{4}}}} \right).$

Conversely, when the voltage at the AC interface 114 is negative, thecontrol module 116 concurrently closes (or turns on) switches 1, 3, 5and 7 to cycle or otherwise circulate the inductor current (i_(L))through the matrix conversion module 108 for a first time period (t₁).The control module 116 subsequently opens (or turns off) switches 5 and7 while maintaining switches 1 and 3 in a closed state to conduct theinductor current (i_(L)) from node 138 to node 132 through the primarywindings 146 and apply a voltage across the primary windings 146, andthereby delivers energy to the DC interface 102 (via secondary windings144 and the energy conversion module 104) for a second time period (t₂).The control module 116 then concurrently closes (or turns on) switches1, 3, 5 and 7 to cycle or otherwise circulate the inductor current(i_(L)) through the matrix conversion module 108 for a third time period(t₃), and subsequently opens (or turns off) switches 1 and 3 whilemaintaining switches 5 and 7 in a closed state to conduct the inductorcurrent (i_(L)) from node 138 to node 132 through the primary windings146 and apply a voltage across the primary windings 146, and therebydelivers energy to the DC interface 102 (via secondary windings 144 andthe energy conversion module 104) for a fourth time period (t₄). As setforth above, the sum of the four time periods correspond to the durationof the PWM cycle, wherein the ratio of the sum of the first time periodand the third time period to the duration of the PWM cycle correspondsto the compensated PWM duty cycle control value, and the ratio of thesum of the second time period and the fourth time period to the durationof the PWM cycle corresponds to the duty cycle (d).

Referring again to FIG. 3, the control process 300 may repeat throughoutoperation of the electrical system 100 to produce a desired DC outputvoltage at the DC interface 102. In this regard, while operating thematrix conversion module 108 to deliver energy to the DC interface 102in accordance with the duty cycle (d) during one PWM cycle, the controlmodule 116 and/or control system 200 repeats the control process 300 todetermine a compensated PWM duty cycle control value for the next PWMcycle, and so on.

To briefly summarize, one advantage of the systems and/or methodsdescribed above is that a feedforward control system may be utilized tooperate a matrix conversion module to achieve a desired DC outputvoltage while at the same time achieving substantially unity powerfactor and low total harmonic distortion at the AC input. As notedabove, a compensation scaling factor is used to increase the duty cyclefor operating the matrix conversion module in a manner that accounts forcomponent losses. As a result, the accuracy and dynamic performance ofthe feedforward control system is improved.

For the sake of brevity, conventional techniques related to electricalenergy and/or power conversion, electrical charging systems, powerconverters, pulse-width modulation (PWM), and other functional aspectsof the systems (and the individual operating components of the systems)may not be described in detail herein. Furthermore, the connecting linesshown in the various figures contained herein are intended to representexemplary functional relationships and/or physical couplings between thevarious elements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in anembodiment of the subject matter.

Techniques and technologies may be described herein in terms offunctional and/or logical block components, and with reference tosymbolic representations of operations, processing tasks, and functionsthat may be performed by various computing components or devices. Itshould be appreciated that the various block components shown in thefigures may be realized by any number of hardware, software, and/orfirmware components configured to perform the specified functions. Forexample, an embodiment of a system or a component may employ variousintegrated circuit components, e.g., memory elements, digital signalprocessing elements, logic elements, look-up tables, or the like, whichmay carry out a variety of functions under the control of one or moremicroprocessors or other control devices.

The foregoing description refers to elements or nodes or features being“connected” or “coupled” together. As used herein, unless expresslystated otherwise, “connected” means that one element/node/feature isdirectly joined to (or directly communicates with) anotherelement/node/feature, and not necessarily mechanically. Likewise, unlessexpressly stated otherwise, “coupled” means that oneelement/node/feature is directly or indirectly joined to (or directly orindirectly communicates with) another element/node/feature, and notnecessarily mechanically. Thus, although the figures may depict oneexemplary arrangement of elements or direct electrical connectionsbetween circuit elements, additional intervening elements, devices,features, or components may be present in an embodiment of the depictedsubject matter. In addition, certain terminology may also be used hereinfor the purpose of reference only, and thus is not intended to belimiting. The terms “first”, “second” and other such numerical termsreferring to structures do not imply a sequence or order unless clearlyindicated by the context.

As used herein, a “node” means any internal or external reference point,connection point, junction, signal line, conductive element, or thelike, at which a given signal, logic level, voltage, data pattern,current, or quantity is present. Furthermore, two or more nodes may berealized by one physical element (and two or more signals can bemultiplexed, modulated, or otherwise distinguished even though receivedor output at a common node).

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

1. An electrical system comprising: an input interface; an outputinterface; a first energy conversion module coupled between the inputinterface and the output interface, the first energy conversion moduleincluding one or more switching elements; and a control module coupledto the first energy conversion module, the input interface, and theoutput interface, wherein the control module is configured to: determinea duty cycle control value for operating the first energy conversionmodule to produce a desired voltage at the output interface; determinean input power error at the input interface; adjust the duty cyclecontrol value in a manner that is influenced by the input power error,resulting in a compensated duty cycle control value; and operate the oneor more switching elements of the first energy conversion module todeliver energy to the output interface with a duty cycle that isinfluenced by the compensated duty cycle control value.
 2. Theelectrical system of claim 1, wherein the control module is configuredto: determine a compensation scaling factor based on the input powererror; and multiply the duty cycle control value by the compensationscaling factor to obtain the compensated duty cycle control value. 3.The electrical system of claim 2, wherein the control module isconfigured to determine the input power error by: determining an inputpower reference for the input interface based on the desired voltage atthe output interface and a measured voltage at the output interface;estimating input power at the input interface, resulting in an estimatedinput power at the input interface; and determining a difference betweenthe input power reference and the estimated input power.
 4. Theelectrical system of claim 3, further comprising: an inductive elementcoupled between the input interface and the first energy conversionmodule; and a capacitive element coupled between the input interface andthe inductive element, the capacitive element being configuredelectrically parallel to the input interface.
 5. The electrical systemof claim 4, wherein the control module is configured to determine theduty cycle control value by: determine an inductor current referencebased on the input power reference; determine an input voltage referencebased on a difference between the inductor current reference and ameasured current through the inductive element; and divide the inputvoltage reference by a measured voltage at the output interface toobtain the duty cycle control value.
 6. The electrical system of claim1, further comprising: a second energy conversion module coupled to theoutput interface; and an isolation module coupled between the firstenergy conversion module and the second energy conversion module, theisolation module providing galvanic isolation between the first energyconversion module and the second energy conversion module.
 7. Theelectrical system of claim 6, further comprising: an inductive elementcoupled between the input interface and the first energy conversionmodule; and a capacitive element coupled between the input interface andthe inductive element, the capacitive element being configuredelectrically parallel to the input interface.
 8. The electrical systemof claim 7, wherein the first energy conversion module comprises amatrix conversion module.
 9. The electrical system of claim 8, whereinthe matrix conversion module comprises: a first node; a second node; athird node; a fourth node; a first switching element coupled between thefirst node and the third node, the first switching element beingconfigured to allow current from the third node to the first node whenthe first switching element is closed; a second switching elementcoupled between the first switching element and the third node, thesecond switching element being configured to allow current from thefirst node to the third node when the second switching element isclosed; a third switching element coupled between the first node and thefourth node, the third switching element being configured to allowcurrent from the fourth node to the first node when the third switchingelement is closed; a fourth switching element coupled between the thirdswitching element and the fourth node, the fourth switching elementbeing configured to allow current from the first node to the fourth nodewhen the fourth switching element is closed; a fifth switching elementcoupled between the second node and the fourth node, the fifth switchingelement being configured to allow current from the second node to thefourth node when the fifth switching element is closed; a sixthswitching element coupled between the fifth switching element and thesecond node, the sixth switching element being configured to allowcurrent from the fourth node to the second node when the sixth switchingelement is closed; a seventh switching element coupled between thesecond node and the third node, the seventh switching element beingconfigured to allow current from the second node to the third node whenthe seventh switching element is closed; and an eighth switching elementcoupled between the seventh switching element and the second node, theeighth switching element being configured to allow current from thethird node to the second node when the eighth switching element isclosed.
 10. The electrical system of claim 9, wherein: the inductiveelement is coupled electrically in series between the first node of thematrix conversion module and a first input node of the input interface;the second node of the matrix conversion module is coupled to a secondinput node of the input interface; the capacitive element is coupledbetween the first input node and the second input node; the isolationmodule comprises a first set of windings coupled between the third nodeand the fourth node and a second set of windings coupled to the secondenergy conversion module, the second set of windings being magneticallycoupled to the first set of windings; and the control module isconfigured to operate the first switching element, the second switchingelement, the third switching element, the fourth switching element, thefifth switching element, the sixth switching element, the seventhswitching element, and the eighth switching element to deliver energy tothe output interface with the duty cycle corresponding to the duty cyclecontrol value.
 11. The electrical system of claim 10, wherein thecontrol module is configured to: determine an input power reference forthe input interface based on the desired voltage at the output interfaceand a measured voltage at the output interface; determine an estimatedinput power at the input interface; determine a compensation scalingfactor based on a difference between the input power reference and theestimated input power; and multiply the duty cycle control value by thecompensation scaling factor to obtain the compensated duty cycle controlvalue.
 12. A method for delivering energy from an input interface to anoutput interface using an energy conversion module coupled between theinput interface and the output interface, the energy conversion moduleincluding one or more switching elements coupled to an inductiveelement, the method comprising: determining an input power reference forthe input interface based on a desired output voltage at the outputinterface; determining a duty cycle control value based on the inputpower reference; determining an input power error based on a differencebetween an estimated input power at the input interface and the inputpower reference; adjusting the duty cycle control value in a manner thatis influenced by the input power error to obtain a compensated dutycycle control value; and operating the one or more switching elements todeliver energy from the input interface to the output interface with aduty cycle influenced by the compensated duty cycle control value. 13.The method of claim 12, further comprising determining a compensationscaling factor based on the input power error, wherein adjusting theduty cycle control value comprises multiplying the duty cycle controlvalue by the compensation scaling factor to obtain the compensated dutycycle control value.
 14. The method of claim 13, further comprisingdetermining the estimated input power based at least in part on ameasured current through the inductive element and a measured voltage atthe input interface.
 15. The method of claim 14, wherein determining theduty cycle control value comprises: determining an inductor currentreference based on the input power reference; determining an inputvoltage reference based on a difference between the inductor currentreference and the measured current through the inductive element; anddividing the input voltage reference by a measured voltage at the DCinterface to obtain the duty cycle control value.
 16. The method ofclaim 15, wherein determining the estimated input power comprisesmultiplying the measured voltage at the input interface by a sum of ameasured current through the inductive element and a measured currentthrough a capacitive element, the capacitive element being configuredelectrically parallel to the input interface.
 17. The method of claim12, the duty cycle corresponding to one minus the compensated duty cyclecontrol value, wherein operating the one or more switching elements todeliver energy from the input interface to the output interface with theduty cycle comprises: determining pulse-width modulation (PWM) commandsignals for operating the one or more switching elements to deliverenergy from the AC energy source to the DC energy source for apercentage of a switching interval, the percentage being equal to theduty cycle; and operating the one or more switching elements inaccordance with the PWM command signals.
 18. An electrical systemcomprising: a direct current (DC) interface; an alternating current (AC)interface; an isolation module including a first set of windingsmagnetically coupled to a second set of windings; a first energyconversion module coupled between the DC interface and the first set ofwindings; a second conversion module coupled to the second set ofwindings, the second conversion module including a plurality ofswitches; an inductive element coupled between the second conversionmodule and the AC interface; and a control module coupled to the secondconversion module, wherein the control module is configured to:determine an input power reference for producing a desired voltage atthe DC interface based on the desired voltage and a measured voltage atthe DC interface; determine an input power error at the AC interfacebased on a difference between an estimated input power at the ACinterface and the input power reference; determine a compensatedpulse-width modulation (PWM) duty cycle control value for operating thefirst energy conversion module based on the input power reference andthe input power error; and operate the plurality of switches of thesecond conversion module in accordance with the compensated PWM dutycycle control value.
 19. The electrical system of claim 18, furthercomprising a capacitive element coupled between the AC interface and theinductive element, the capacitive element being configured electricallyparallel to the AC interface, wherein the control module is configuredto determine the estimated input power at the AC interface based on ameasured voltage at the AC interface, a measured current thought theinductive element, and a measured current through the capacitiveelement.
 20. The electrical system of claim 19, wherein the controlmodule is configured to: determine an uncompensated PWM duty cyclecontrol value based on the input power reference; determine acompensation scaling factor based on the input power error; and multiplythe uncompensated PWM duty cycle control value by the compensationscaling factor to obtain the compensated PWM duty cycle control value.